Development of rotating tube reactor for biodiesel production from palm oil

Abstract

Rotating tube reactor (RTR), one of process intensification technologies, could highly increase the mixing performance and generate sufficient heat for biodiesel production. This research explored the optimum condition, essential characteristics of hydrodynamic regime and residence time distribution inside the rotating tube reactor (RTR) to enhance the biodiesel production rate using alkali-catalyzed transesterification. The operating condition of this RTR was 6:1 methanol-to-oil molar ratio, total flowrate of 30 mL/min and rotational speed of 1,000 rpm at room temperature, giving the highest biodiesel yield of 97.5% with yield efficiency of 3.75 × 10-3 g/J and the quality of biodiesel achieving the ASTM specification. Two dimensionless numbers, including rotating Reynolds number (Rer) and Taylor number (Ta), as well as torque, were used to determine the hydrodynamic regime in this RTR which can be related to biodiesel yield. This indicates that the modulated wavy vortex flow (MWVF) is required to promote biodiesel yield in the RTR. Whereas the increment values of Rer, Ta and torque associated with the turbulent Taylor vortex flow regime produced more extra heat to enhance methanol vaporization rate, leading to reduced biodiesel yield. The residence time distribution (RTD) of RTR was also found in the nonideal flow pattern. The peak of RTD, mean residence time and dispersion number could reveal turbulent mixing degree in the RTR. High turbulent mixing obviously appears at a higher flowrate and higher rotational speed. However, at excessive flowrate, the role of axial mixing was more significant than that of the radial mixing, resulting in the reduction of turbulent flow. Moreover, the RTR combined with a solar-bicycle generator system was developed to demonstrate the possible use of alternative energy for economical and sustainable production of biodiesel.